Seperated colour histogram

[ultramol]

Can anyone tell me why the red green and blue histograms at the end of stacking in DSS are all seperate from each other. I only ask as when I have looked at tutorials they allways seem to be together. Also why do my bright stars in my photos not have diffraction spike on them when others seem to have them. Many thanks.......Geoff

[jambouk]

Are you selecting "align RGB" prior to stacking?

No idea about spikes.

James

[chrisg18]

I think the diffraction spikes are caused because of the secondary mirror spider veins in a ref scope

[ultramol]

Are you selecting "align RGB" prior to stacking?

No idea about spikes.

James

Is this command in DSS, if it is then I didnt select it

[D4N]

If you use a refractor you won't get diffraction spikes. These are created in Newtonian style telescopes as the secondary mirrors supports scatter some of the incoming light.

You can also create them in software or by putting some fine thread in a cross over the end of your scope.

The different colour histograms don't need to line up and RGB align is not designed for that. RGB align shifts misaligned images, for example if your stars are split up with red shadows one side and blue the other.

It is quite normal if for example you take an image of a nebula for there to be far more red in the image than any other colour. Hence the red channel will be more exposed and wider.

Sky glow from sodium lamps can also cause the red to over expose compared to the green and blue shifting it to the right.

When you post process the image you will be tweaking these when you do your curves and they may get closer together.

Edit: just noticed your equipment says you have a 200P, if this is the scope you are using you should get spikes if the stars are bright enough and the exposure time is long enough.

/Dan

Sent from my iPad using Tapatalk

[Freddie]

If you use a refractor you won't get diffraction spikes. These are created in Newtonian style telescopes as the secondary mirrors supports scatter some of the incoming light.

You can also create them in software or by putting some fine thread in a cross over the end of your scope.

The different colour histograms don't need to line up and RGB align is not designed for that. RGB align shifts misaligned images, for example if your stars are split up with red shadows one side and blue the other.

It is quite normal if for example you take an image of a nebula for there to be far more red in the image than any other colour. Hence the red channel will be more exposed and wider.

Sky glow from sodium lamps can also cause the red to over expose compared to the green and blue shifting it to the right.

When you post process the image you will be tweaking these when you do your curves and they may get closer together.

Edit: just noticed your equipment says you have a 200P, if this is the scope you are using you should get spikes if the stars are bright enough and the exposure time is long enough.

/Dan

Sent from my iPad using Tapatalk

With reference to the RGB align comment above, I think you are confusing what something like Registax does and what DSS is trying to do.  In regi, it will in effect move the R,G and B elements to get better alignment when, as you say, you get a colour that is not aligned properly. What DSS is trying to do is better align the peaks of the 3 histos. In RGB you want to try and align the top left of the histo peaks and the different colour intensity will be brought out by the different shapes of the different colour curves. 

[ultramol]

Thanks all for your help, much appreciated....Regards.....geoff

[D4N]

With reference to the RGB align comment above, I think you are confusing what something like Registax does and what DSS is trying to do. In regi, it will in effect move the R,G and B elements to get better alignment when, as you say, you get a colour that is not aligned properly. What DSS is trying to do is better align the peaks of the 3 histos. In RGB you want to try and align the top left of the histo peaks and the different colour intensity will be brought out by the different shapes of the different colour curves.

That isn't what it says on the DSS website. Background calibration will result in what you are saying though if you use RGB Channels Calibration but this is at the expense of losing some saturation.

http://deepskystacker.free.fr/english/technical.htm#Stacking

/Dan

Sent from my iPad using Tapatalk

[Freddie]

I think the confusion is coming from the terminology being used and what the OP is referring to.

There is an "align RGB channels in final image" tick box on the stacking parameters results tab. That will align the individual channels to try and remove the misalignment of the three different colour on the final image i.e the red/blue stars you describe.

The background calibration will attempt to do as I have described and match up the positions of the histograms, which is what I believe the OP was referring to. Selecting one of these rather than neither would be best as it would allow a kapps-S stacking with the advantages that brings (assuming you have 10+ subs)

Hope that helps clear things up.

[D4N]

The terminology is indeed confusing. Personally I preferred to sort out the channels myself in post processing as DSS tends to be a bit heavy handed.

I've not used it in a while now, Nebulosity is much easier to get on with

/Dan

Sent from my iPad using Tapatalk

[Freddie]

Yep, I now use AA5 so had to remind myself about the DSS specifics.

The disadvantage of not selecting one of those options is the inability to then use a Kappa stack.

[ultramol]

I used the rgb setting and immediately got better result. Before no matter what I did I could not get the nebula to show up. After the change I got this.....It needs more work but at least I can see it now, thank you all very much